501 research outputs found

### Coordinates with Non-Singular Curvature for a Time Dependent Black Hole Horizon

A naive introduction of a dependency of the mass of a black hole on the
Schwarzschild time coordinate results in singular behavior of curvature
invariants at the horizon, violating expectations from complementarity. If
instead a temporal dependence is introduced in terms of a coordinate akin to
the river time representation, the Ricci scalar is nowhere singular away from
the origin. It is found that for a shrinking mass scale due to evaporation, the
null radial geodesics that generate the horizon are slightly displaced from the
coordinate singularity. In addition, a changing horizon scale significantly
alters the form of the coordinate singularity in diagonal (orthogonal) metric
coordinates representing the space-time. A Penrose diagram describing the
growth and evaporation of an example black hole is constructed to examine the
evolution of the coordinate singularity.Comment: 15 pages, 1 figure, additional citation

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### Astrophysical cosmology

The last several years have seen a tremendous ferment of activity in astrophysical cosmology. Much of the theoretical impetus has come from particle physics theories of the early universe and candidates for dark matter, but what promise to be even more significant are improved direct observations of high z galaxies and intergalactic matter, deeper and more comprehensive redshift surveys, and the increasing power of computer simulations of the dynamical evolution of large scale structure. Upper limits on the anisotropy of the microwave background radiation are gradually getting tighter and constraining more severely theoretical scenarios for the evolution of the universe. 47 refs

### On the black hole limit of rotating discs and rings

Solutions to Einstein's field equations describing rotating fluid bodies in
equilibrium permit parametric (i.e. quasi-stationary) transitions to the
extreme Kerr solution (outside the horizon). This has been shown analytically
for discs of dust and numerically for ring solutions with various equations of
state. From the exterior point of view, this transition can be interpreted as a
(quasi) black hole limit. All gravitational multipole moments assume precisely
the values of an extremal Kerr black hole in the limit. In the present paper,
the way in which the black hole limit is approached is investigated in more
detail by means of a parametric Taylor series expansion of the exact solution
describing a rigidly rotating disc of dust. Combined with numerical
calculations for ring solutions our results indicate an interesting universal
behaviour of the multipole moments near the black hole limit.Comment: 18 pages, 4 figures; Dedicated to Gernot Neugebauer on the occasion
of his 70th birthda

### Light Quark Simulations With FLIC Fermions

Hadron masses are calculated in quenched lattice QCD in order to probe the
scaling behavior of a novel fat-link clover fermion action in which only the
irrelevant operators of the fermion action are constructed using APE-smeared
links. Light quark masses corresponding to an m_pi / m_rho ratio of 0.35 are
considered to assess the exceptional configuration problem of clover-fermion
actions. This Fat-Link Irrelevant Clover (FLIC) fermion action provides scaling
which is superior to mean-field improvement and offers advantages over
nonperturbative improvement, including reduced exceptional configurations.Comment: 3 pages, 2 figures, Lattice2002(QCD Spectrum and Quark Masses

### Boundary value problems for the stationary axisymmetric Einstein equations: a disk rotating around a black hole

We solve a class of boundary value problems for the stationary axisymmetric
Einstein equations corresponding to a disk of dust rotating uniformly around a
central black hole. The solutions are given explicitly in terms of theta
functions on a family of hyperelliptic Riemann surfaces of genus 4. In the
absence of a disk, they reduce to the Kerr black hole. In the absence of a
black hole, they reduce to the Neugebauer-Meinel disk.Comment: 46 page

### Non-perturbative scalar gauge-invariant metric fluctuations from the Ponce de Leon metric in the STM theory of gravity

We study our non-perturbative formalism to describe scalar gauge-invariant
metric fluctuations by extending the Ponce de Leon metric.Comment: accepted in Eur. Phys. J.

### First law of black hole mechanics in Einstein-Maxwell and Einstein-Yang-Mills theories

The first law of black hole mechanics is derived from the Einstein-Maxwell
(EM) Lagrangian by comparing two infinitesimally nearby stationary black holes.
With similar arguments, the first law of black hole mechanics in
Einstein-Yang-Mills (EYM) theory is also derived.Comment: Modified version, major changes made in the introduction. 14 pages,
no figur

### Density Perturbations in the Ekpyrotic Scenario

We study the generation of density perturbations in the ekpyrotic scenario
for the early universe, including gravitational backreaction. We expose
interesting subtleties that apply to both inflationary and ekpyrotic models.
Our analysis includes a detailed proposal of how the perturbations generated in
a contracting phase may be matched across a `bounce' to those in an expanding
hot big bang phase. For the physical conditions relevant to the ekpyrotic
scenario, we re-obtain our earlier result of a nearly scale-invariant spectrum
of energy density perturbations. We find that the perturbation amplitude is
typically small, as desired to match observation.Comment: 36 pages, compressed and RevTex file, one postscript figure file.
Minor typographical and numerical errors corrected, discussion added. This
version to appear in Physical Review

### Relativistic dust disks and the Wilson-Mathews approach

Treating problems in full general relativity is highly complex and frequently
approximate methods are employed to simplify the solution. We present
comparative solutions of a infinitesimally thin relativistic, stationary,
rigidly rotating disk obtained using the full equations and the approximate
approach suggested by Wilson & Mathews. We find that the Wilson-Mathews method
has about the same accuracy as the first post-Newtonian approximation.Comment: 4 Pages, 5 eps-figures, uses revtex.sty. Submitted to PR

### Non-Commutative Inflation

We show how a radiation dominated universe subject to space-time quantization
may give rise to inflation as the radiation temperature exceeds the Planck
temperature. We consider dispersion relations with a maximal momentum (i.e. a
mimimum Compton wavelength, or quantum of space), noting that some of these
lead to a trans-Planckian branch where energy increases with decreasing
momenta. This feature translates into negative radiation pressure and, in
well-defined circumstances, into an inflationary equation of state. We thus
realize the inflationary scenario without the aid of an inflaton field. As the
radiation cools down below the Planck temperature, inflation gracefully exits
into a standard Big Bang universe, dispensing with a period of reheating.
Thermal fluctuations in the radiation bath will in this case generate curvature
fluctuations on cosmological scales whose amplitude and spectrum can be tuned
to agree with observations.Comment: 4 pages, 3 figure

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